This invention relates to the field of machine generation of animation and, more particularly, to a method and apparatus for generating sequences of frames on a two-dimensional screen that are representative of three-dimensional animated figures.
Animated films are in widespread use for educational and entertainment purposes. Animated films of reasonably high quality have traditionally been very expensive to make. The initial creative work includes generation of a basic story, a sound track, and basic character designs. Typically, a schedule is generated which describes the movements and timings of each scene to be produced, and layout sketches and "key" drawings are made which define the overall design of each scene. It has been generally observed that at this point most of the creative design work has already been done. The so-called "key" drawings or frames are still frames which show extremes of action. In the traditional animation procedure, people known as "in-betweeners" are employed to sketch frames which fill in the action between key frames. After in-betweens are sketched by hand, the hand-drawn pictures are typically transferred onto celluloid-acetate sheets and are then painted in by hand. Much labor is involved in obtaining the in-betweens, which typically comprise the majority of frames of the final work product. These tasks render the production of animated films an extremely expensive proposition. An advantage of the traditional animation process, however, is that the animator has virtually complete artistic freedom and control over the resulting film; i.e. anything that is drawn can be made to move in a desired fashion so natural-looking motion can generally be achieved.
In recent years, the field of machine generation of animation has made great strides. Advanced computer graphics techniques have improved the speed and quality of computer-generated animation. Computers can aid artistic animators in many ways, including automatic generation of in-between frames by interpolation of lines appearing in successive key frames. A technique of this type is described, for example, in an article entitled "Towards a Computer Animating Production Tool" by N. Burtnyk and M. Wein which appeared in the proceedings of Eurocomp Conference, Brunel - United Kingdom, May 1974.
It is known in the computer graphics art that three-dimensional representation of animated figures can be stored as a set of three dimensional points, and appropriate transformations can be used to automatically compute the projection of the three-dimensional figures onto a two dimensional surface, so that two dimensional computer generated animation images can be presented on a conventional two-dimensional screen. Three dimensional figures have also been represented in joint and limb configuration.
Representative prior art patents relating to techniques such as computer-generation of in-between frames and three-dimensional animation are as follows: U.S. Pat. Nos. 3,364,382; 3,523,389; 3,585,628; 3,603,964; 3,700,792; 3,723,803; 3,747,087; 3,792,243; 3,883,861; 3,917,955; 3,885,096; 4,017,680; 4,127,849; 4,189,743; 4,189,744; 4,200,867; 4,213,189.
As above-stated, the automatic machine generation of in-between frames can greatly reduce the amount of time and effort that is necessary to generate a series of animated frames. Particularly when dealing with three-dimensional animation, however, the automatic generation of in-between frames can tend to result in unnatural motion of the three dimensional figures.
It is among the objects of the present invention to provide a method and apparatus for generating frames of three-dimensional animated sequences which have natural-looking motion. It is a further object to provide an animator with a high degree of flexibility in obtaining the desired appearance of motion of figures with minimal labor.